[Wien] structure optimization using LAD+U

Dear all, I am working on the magnetic properties of rare earth?iron compounds. I have a question in structure optimization. How to set the U and J parameters when using LDA+U method, since U and J can?t be calculated by ab initio way? So I just set U=J=0. If it is reasonable, then is it

[Wien] structure optimization using LAD+U

I am working on the magnetic properties of rare earth?iron compounds. I have a question in structure optimization. How to set the U and J parameters when using LDA+U method, since U and J can?t be calculated by ab initio way? So I just set U=J=0. If it is reasonable, then is it

[Wien] structure optimization using LAD+U

Dear H. Pang, there is a paper about U determination by Madsen and Novak on the wien2k page: http://www.wien2k.at/reg_user/textbooks/ They suggest that you put J=0 and choose some positive value of U. Also there was a discussion on the list about U determination some months ago, search the list.